Challenges and Prospects Towards Developing Emerging Antimony and Bismuth-Based Chalcogenide for Next Generation, Earth Abundant Photovoltaics

The emergence of new PV applications in the society requires the design of materials and devices with a different set of properties. At this scale, for a new photovoltaic (PV) technology is not sufficient to be only competitive with the Si and CdTe technologies in efficiency and reliability but one should also rely on green, environmentally friendly, and earth-abundant materials. An emerging class of highly promising PV materials currently under widespread investigation in the PV community are the inorganic antimony-and bismuth-based chalcogenide compounds. The excellent intrinsic material properties of these compounds allowed to rapidly approach 8-10% conversion efficiency, opening a new chapter in PV research, full of new possibilities but also scientific challenges. This talk will discuss the latest achievements in bismuth- and antimony-based thin film solar cell technology with the main emphasis on Sb₂Se₃ and Bi₂S₃ compounds. I will summarize the knowns and unknowns of their defect chemistry, including highlights of unique optoelectronic characteristics that are not yet fully explained. The discussion will highlight the progress achieved in our group, toward growth of high-quality Sb₂Se₃ and Bi₂S₃ absorber films and solar cells by rapid, high-volume, and in-line close-spaced sublimation and vapor transport deposition techniques. Special emphasis will be put on the key processing strategies to optimize absorber material properties (doping and alloying), understanding of buried interfaces and push the boundaries of understanding and performance. A thorough look at the formation chemistry and shed light on some of the synthesis and doping challenges, potential doping elements, the impact this has on carrier density and the impact on solar cell performance.